This invention relates generally to magnetic disk data storage systems, and more particularly to inductive write heads for magnetic data storage media.
Magnetic disk drives are used to store and retrieve data for digital electronic apparatus such as computers. In FIGS. 1A and 1B, a magnetic disk data storage systems 10 of the prior art includes a sealed enclosure 12, a disk drive motor 14, a magnetic disk 16, supported for rotation by a drive spindle S1 of motor 14, an actuator 18 and an arm 20 attached to an actuator spindle S2 of actuator 18. A suspension 22 is coupled at one end to the arm 20, and at its other end to a read/write head or transducer 24. The transducer 24 typically includes an inductive write element with a sensor read element (which will be described in greater detail with reference to FIG. 1C). As the motor 14 rotates the magnetic disk 16, as indicated by the arrow R, an air bearing is formed under the transducer 24 causing it to lift slightly off of the surface of the magnetic disk 16, or, as it is termed in the art, to "fly" above the magnetic disk 16. Alternatively, some transducers, known as "contact heads," ride on the disk surface. Various magnetic "tracks" of information can be read from the magnetic disk 16 as the actuator 18 causes the transducer 24 to pivot in a short arc as indicated by the arrows P. The design and manufacture of magnetic disk data storage systems is well known to those skilled in the art.
FIG. 1C depicts a magnetic read/write head 24 including a write element 26 and a read element 28. The edges of the write element 26 and read element 28 also define an air bearing surface ABS, in a plane 29, which faces the surface of the magnetic disk 16 shown in FIG. 1A and 1B.
The read element 28 includes a first shield 36, an intermediate layer 31, which functions as a second shield, and a read sensor 40 that is located between the first shield 36 and the second shield 31 and suspended within a dielectric layer 37. The most common type of read sensor 40 used in the read/write head 30 is the magnetoresistive sensor which is used to detect magnetic field signals from a magnetic medium through changing resistance in the read sensor.
The write element 26 is typically an inductive write element. The intermediate layer 31 is shared between the read element 28 and the write element 26, forming a first pole of the write element 26. With a second pole 32, the first pole 31 forms a yoke 38. A write gap 30 is formed between the first pole 31 and the second pole 32. Specifically, the write gap 30 is located adjacent to a portion of the first pole and second pole which is sometimes referred to as the yoke tip region 33. The write gap 30 is filled with a non-magnetic material 39. Also included in write element 26, is a conductive coil 34 that is positioned within a dielectric medium 35. The conductive coil 34 of FIG. 1C is formed of a first coil C1 and a second coil C2. As is well known to those skilled in the art, these elements operate to magnetically write data on a magnetic medium such as a magnetic disk 16.
In FIG. 1D, a view taken along line 1D--1D of FIG. 1C (i.e., perpendicular to the plane 29 and therefore perpendicular to the air bearing surface ABS) further illustrates the structure of the write element 28. As can be seen from this perspective, a pole width W of the first pole 31 and second pole 32 in the yoke tip region 30 are substantially equal. A parameter of any write element is its trackwidth which affects its performance. In the configuration of FIG. 1D, the trackwidth is defined by the pole width W.
FIGS. 1E and 1F show two views of another prior art read/write head. The read element 28 of FIG. 1E is substantially the same as in the read/write head of FIG. 1C. However, above and attached to the first pole 31, is a first yoke pedestal Y1P in the yoke tip region 33, abutting the ABS. In addition, a second yoke pedestal Y2P is disposed above and aligned with the first yoke pedestal Y1P. Further, the second yoke pedestal Y2P is adjacent to the second pole 32. The write gap 30 is formed between the first and second yoke pedestals Y1P and Y2P.
The write element 26 of the prior art is shown in FIG. 1F as viewed along the line 1F--1F of FIG. 1E. Here it can be seen that the first and second yoke pedestals Y1P and Y2P have substantially equal pedestal widths Wp which are smaller than the pole width W of the first and second poles 31 and 32 in the yoke tip region 33. In this configuration, the trackwidth of the write element 28 is defined by the width Wp.
An inductive write head such as those shown in FIGS. 1C-1F operates by inducing a magnetic flux in the first and second pole. This can be accomplished by passing a writing current through the conductive coil 34. The write gap 30 allows the magnetic flux to fringe (thus forming a gap fringing field) and impinge upon a recording medium that is placed near the ABS. Thus, the strength of the gap field is a parameter of the write element performance. Other performance parameters include the non-linear transition shift (NLTS), which arises from interbit magnetostatic interactions that occur during the write process, and overwrite.
The amount of time that it takes the magnetic flux to be generated in the poles by the writing current (sometimes termed the "flux rise time") is a critical parameter also, especially for high-speed write elements. In particular, the smaller the flux rise time, the faster the write element can record data on a magnetic media (i.e., a higher data rate). The extended flux rise time is an indicator of eddy current losses and head saturation in the write element. Thus, high data rate applications with large linear bit density and large track density can be accommodated by a writer having a large gap field and low eddy current loss.
It has been found that the yoke length YL of the second pole 32 influences the flux rise time, as is shown by the curves in the graph of FIG. 2A. The corresponding impact of yoke length on data rate can be seen with reference to the curves of FIG. 2B. As can be seen in FIGS. 2A and 2B, the flux rise time, and therefore data rate, of a typical second pole of 35% FeNi can be improved with lamination. However, such lamination can increase the fabrication process complexity, for example increasing cycle time as well as cost of fabrication.
It has also been found that materials with higher electrical resistivity .rho. exhibit smaller flux rise times, which indicates that using such materials can reduce eddy current loss in a write element. Other material properties desired in a write material include high saturation magnetic flux density Bs, low saturation magnetostriction .lambda.s, and good corrosion resistance.
Materials that have been used to form the poles in write elements include NiFe, CoFe, CoNiFe, CoZrTa, and FeN. The saturation magnetic flux density, saturation magnetostriction .lambda.s, and corrosion resistance of these materials are listed in the table of FIG. 3. Higher Fe concentration in NiFe alloy does enhance its saturation magnetic flux density Bs, but the magnetostriction .lambda.s of the resultant NiFe alloy increases rapidly. For example, Ni.sub.45 Fe.sub.55 has Bs and .lambda.s values of 15.5 kGauss and 20.times.10.sup.-6, respectively. In addition, the NiFe alloy family has low electrical resistivity which can inhibit high speed applications because of high eddy current losses. CoFe and CoNiFe also suffer from low electrical resistivity. Also, while Fe-based nitride films and their derivatives can have high Bs values when the nitrogenized films are in crystallized bcc phase, they require film lamination to overcome their low electrical resistivity for high data rate applications. As an additional option, CoZrTa, having a relatively large electrical resistivity, can be used. However, CoZrTa exhibits poor corrosion resistance and is therefore less desirable for write element pole use. For example, the corrosion resistance of CoZrTa is exemplified in the graphs of FIGS. 4A and 4B which show Tafel plots using 0.01 M NaCl and Na.sub.2 SO.sub.4 electrolytes, respectively.
Thus, what is desired is an improved write element design that can effectively operate at high speeds while significantly resisting corrosion. Further, such a write element that can write at high data densities is desired.